Conversion of hydrocarbon oils



Feb. 4, 1936. G. D, WHITE CONVERSION OF HYDROCARBON OILS Filed April 30,1934 a INVENTOR.

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Patented Feb. 4, 1936 UNITED STATES PATENT OFFICE George D. White, PortArthur, Tex., assignor to The Texas Company, New York, N. Y., acorporation of Delaware Application April 30, 1934, Serial No. 723,065

2 Claims.

This invention relates to the conversion of hydrocarbon oils and hasreference to a method of treating the oil in which selected fractionshaving different boiling ranges are first separated and the separatedfractions subjected to different heat treatments under optimumconditions to produce the desired end products.

One of the principal objects of the invention is to improve the methodof heat treating the hydrocarbons so as to reduce coke formation in theheating unit without lowering the efiiciency of the process or thequality of the motor fuel produced.

In accordance with my invention, a selected clean cycle stock,preferably withdrawn from a secondary fractionating zone, is heattreated under relatively drastic temperature conditions,

such as for example vapor phase cracking conditions, and thereafterimmediately commingled with relatively cooler and heavier hydrocarbonoil stock, preferably comprising the bottoms of a primary fractionatingand distilling zone, into which fresh oil may be charged. The commingledhydrocarbons are then passed through an additional heating coil in whichthey are subjected to less drastic temperature conditions, and are thenpassed to a suitable chamber for separating the reaction products intovapors and unvaporized residual material, and in which additionalcracking may take place.

Other and more detailed objects and advantages of the invention willappear in the description hereinafter.

With the above objects and advantages in view, the invention will bebest understood by referring to the accompanying drawing which is aschematic illustration of an apparatus which may be employed forcarrying the invention into effect.

Referring to the drawing, the apparatus in general comprises a furnaceID, a separating or cracking chamber H, a primary fractionating anddistilling tower l2, and a secondary fractionating tower I3, togetherwith the necessary connecting pipe lines provided with suitable pumpsand valves for causing the hydrocarbons to flow in the mannerhereinafter described. It is to be understood that in addition to thatshown, the apparatus in its entirety will include other conventionalequipment and appurtenances normally making up a complete conversionunit such as temperature and pressure indicating and control devices formaintaining and. controlling the temperature and pressure conditions inthe unit. It is also to be understood that the apparatus shown may beemployed in conjunction with other apparatus for carrying out furtherseparation and purification of the end products produced in theapparatus illustrated.

In carrying out my invention a clean condensate stock formed byfractionating vapors in the secondary fractionating tower I3 iswithdrawn from the latter tower through line H! provided with a pump i5which forces the withdrawn condensate through the heating coil I 6located adjacent the side walls in the radiant heat section of thefurnace Ill. The condensate passing through the wall tubes is subjectedto cracking temperature conditions for carrying out the conversiontreatment. For example, the condensate during its passage through thetubes may be heated to temperatures ranging from 900 or 950 to 1050 F.The oil thus heated is withdrawn from the radiant heat section of thefurnace,

preferably before final conversion has taken place, and the oil thusheated is passed through the line I? and commingled immediately in linel8 with a cooler hydrocarbon stream withdrawn from the bottom' of theprimary fractionating tower l2 through line IS. The combined stream isthen passed through line l8 into a heating coil 20 wherein furtherconversion of the clean lower boiling condensate and an initialconversion or viscosity breaking of the heavier stock from the bottom ofthe primary fractionating tower I2 is effected. The reaction productsfrom the heating coil 28 are discharged through transfer line 2| intothe chamber ll wherein additional cracking may be accomplished. Asillustrated, a portion of the heated condensate from the radiant zone ofthe furnace may be by-passed through line 22 around the heating coil 20and introduced into the transfer line 2| leading from the coil 20 to thechamber II.

The oil in the chamber II is separated into vapors and unvaporized.constituents. The vapors are withdrawn from the chamber ll through theline 23 and introduced into the primary fractionating tower I2 which maybe provided with suitable cooling and fractionating elements. Theunvaporized residue is withdrawn from the chamber ll through line 24 anddischarged from the system, being passed to suitable storage receptaclesor subjected to further treating as desired.

The vapors passing through the tower I2 are P subjected to fractionationto condense the higher boiling constituents therefrom. The uncondensedvapors from tower 12 are then passed through the line 25 to thesecondary fractionating tower [3 where they are subjected to finalfractionation. The vapors from the top of the secondary fractionatingtower l3 which contain the gasoline constituents are Withdrawn throughline 26 and passed to a condenser 21 for condensing the gasolineconstituents, after which they are passed to a gas separator 28 forseparating the gases from the gasoline distillate. Gasoline distillatefrom the separator 28 is then withdrawn through line 29 and passed tosuitable storage receptacles or subjected to further treatment asdesired. As shown, a part of the gasoline may be returned to thefractionating tower l3 through line 3| to serve as a cooling andrefluxing agent.

As illustrated, fresh charging stock, with or without preheating, may beintroduced either into the separating chamber ll or the primaryfractionating tower IE, or into both of these chambers. For example thefresh charging stock, which may be a crude, reduced crude, or heavy(dirty) gas oil, may be introduced into the system through line 32provided with a pump 33. The fresh charge may be preheated by passing inseries through a heat exchange coil 34 located in the top of thesecondary fractionating tower l3, thence by means of line 35, throughheating coil 36 located in the economizer section of the furnace, andthen discharged into either or both chambers I! and I2. Aportion or allof the fresh charge may by-pass either or both the heating coils 34 and36 through lines Bl and 38 respectively, and introduced into chambers Hand 12. Under normal operation I prefer to introduce a major portion ofthe fresh charging stock into the primary fractionating and distillingtower 12, so that the unvaporized constituents of the charge will becombined with condensate formed in the chamber and will be subjected toa mild conversion treatment in the nature of a viscosity breakingoperation in coil 20, as hereinbefore described. The fresh chargeintroduced into tower l2 will be further heated by the more highlyheated vapor products undergoing fractionation and will be stripped ofwhatever lighter constituents, such as gasoline, kerosene, or light gasoil which may be present in the original charge. As an alternative aportion or all of the fresh charge may be introduced into chamber l l inwhich case the charge will be distilled and subjected to cracking inchamber II to the final residual products by the heat of the more highlyheated products from the heating coils l6 and 20.

For simplicity only a single separating or cracking chamber II and asingle primary fractionating and distilling tower l2 have beenillustrated. It will be understood, however, that any desired number ofthese chambers connected either in series or parallel may be employed ifdesired.

The following specific example of operating conditions to be employedmay be helpful in attaining a clear understanding of my invention. It isunderstood, however, that the invention is not limited to the specificexample given as the desired operating conditions will vary, dependingupon external factors, such as the character of the charging stock anddesired end point of the gasoline produced. However, with theinformation here contained the desired operating conditions in eachcircumstance will be evident to those familiar with this art.

As before mentioned the clean condensate stock from the bottom of thesecondary fractionating tower l3 may be brought to a temperature rangingfrom about 900 or 950 to l050 F. during its passage through the heatingcoil I6. The temperature and time of treatment may be such as to causefrom about fifteen or twenty to about thirty percent (or even higher)conversion of the stock during its passage through the coil I6.

The heavier cycle stock withdrawn from the bottom of the primaryfractionating tower l2 before merging with the hot products from coil 16may be at a temperature ranging from 650 to 750 F. and the combinedstream after merging, but before passing through coil 20, may be at atemperature ranging from about 750 to about 850 F. Sufficient heat maybe supplied to the combined stream during its passage through theheating coil 20 to raise the temperature of the oil to a temperature offrom about 800 to about 900 F., or higher, or only sufficient heat addedto supply the normal heat losses resulting from endothermic reactions ofthe oil within the coil without any substantial increase in temperatureof the oil.

The fresh or raw oil introduced into the system, from line 32, may bepreheated to any desired degree, for example up to from 400 to 600 F.However, it may be heated to or subjected to a substantial crackingtemperature, say 750 to 875 F., during its flow through the coil 36. Inthis event it is preferable to discharge the oil from the coil 36 intothe distilling and cracking chamber H wherein it undergoes furtherconversion in admixture with the hot products from coils l6 and 20.

The pressure conditions may be maintained substantially uniformthroughout the whole apparatus except for normal friction lossesresulting from the passage of the products through the system, or ifdesired, pressure in the furnace coils l6 and 20 may be maintainedhigher than that in the remaining portion of the apparatus by providinga reducing valve in the line 2 l. The pressure conditions may vary overthe normal range of pressure conditions employed in the treatment ofhydrocarbon oils such as for example between and 1000 lbs. per squareinch. The invention, however, is particularly adaptable to relativelylow pressure operations such as for example from 100 to 400 lbs. persquare inch.

While the preferred embodiment has been described for purposes ofillustration, it is to be 1 understood that the invention embraces suchother modifications or variations as come within the scope and spiritthereof and that the invention is not to be limited except as necessaryto distinguish from prior art.

I claim:

1. In a process for converting higher boiling hydrocarbons into lowerboiling hydrocarbons suitable for motor fuel, wherein cracked residualproducts are withdrawn from the system without being recirculatedthrough a heating coil; the improvement which comprises passing acombined stream of oil of the character hereinafter specified through aheating coil maintained at a cracking temperature, maintaining the oilin said coil for a time sufficient to effect conversion of higherboiling hydrocarbons into lower boiling hydrocarbons, discharging theconverted products from said coil into an enlarged chamber whereinseparation of the vapors and unvaporized residual products is effected,maintaining the oil in said enlarged chamber at an active crackingtemperature to cause further cracking thereof, withdrawing all of theresidual products from the chamber and discharging them from thesystern, separating the vapors by fractionation into a vapor fraction, ahigher boiling condensate fraction and a lower boiling condensatefraction, separately condensing the vapor fraction to produce thedesired distillate product, heating the lower boiling condensatefraction in a separate heating coil to a cracking temperature materiallyhigher than that for said first mentioned heating coil to effectsubstantial conversion of said lower boiling fraction, thereafterimmediately combining a portion of said highly heated lower boilingfraction with said higher boiling fraction, passing the combined streamto said first mentioned heating coil, and passing the remainder of saidhighly heated lower boiling fraction directly to said enlarged chamberto aid in maintaining a cracking temperature therein.

2. In a process for converting higher boiling hydrocarbons into lowerboiling hydrocarbons suitable for motor fuel, wherein cracked residualproducts are withdrawn from the system without being recirculatedthrough a heating coil; the improvement which comprises passing acombined stream of hydrocarbons of the character hereinafter specifiedthrough a heating coil, subjecting the hydrocarbons during their passagethrough the coil to a cracking temperature for a period sufficient toeffect conversion of higher boiling hydrocarbons into lower boilinghydrocarbons, introducing the resulting products from said heating coilinto an enlarged chamber wherein separation of vapors and unvaporizedresidual products is efiected, maintaining the oil in said enlargedchamber at an active cracking temperature to cause further crackingthereof, subjecting the vapors from said enlarged chamber to progressivefractionation in primary and secondary fractionating zones to separatesaid vapors into a vapor fraction, a lower boiling condensate fractionand a higher boiling condensate fraction, introducing fresh chargingstock into said primary fractionating zone wherein unvaporizedconstituents of the charging .stock is admixed with said higher boilingcondensate fraction, separately condensing the light vapor fraction toproduce the desired distillate product, separately heating said lowerboiling condensate fraction to a temperature materially higher than thefinal temperature of the hydrocarbons in said first named heating coiland for a period of time sufficient to effect a substantial conversionof the lower boiling condensate fraction into hydrocarbons suitable formotor fuel, thereafter immediately combining a portion of the convertedproducts of said lower boiling condensate fraction with the mixture ofunvaporized constituents of the fresh oil and the higher boilingcondensate fraction withdrawn from said primary fractionating zone,passing the combined stream to the first mentioned heating coil, andpassing the remainder of said highly heated lower boiling fractiondirectly into said enlarged chamber to aid in maintaining a crackingtemperature therein. GEORGE D. WHITE.

